First of all twitter's growth is slowing, so its not very apt to compare them to google. And the same thing may start happening to Facebook in a few years (as people are notoriously fickle with social media sites - which depend on mass adoption - not innovation). I think google is doing the right thing - they are sticking to what they know instead of trying to 'build around the web' and become another Microsoft (who tries to make 'their own version of everything' example - Silverlight).